1. Field of the Invention
This invention relates to a tibial component for a replacement knee prosthesis and to a total knee prosthesis incorporating such a tibial component.
2. Description of the Prior Art
It is known to provide shock absorbers in total joint prostheses as shown, for example, in European Patent Application No. 83033081 (Publication No. 0 466 926) in which impact absorbers are provided on the tibial component. The impact absorbers are provided across the tibial component to provide shock absorbing for both the medial and lateral bearing components.
It is also known to provide menisci, that is to say, moving plastic components typically made of polyethylene between a metal tibial tray and a metal femoral component that are not locked in place as normal plastic tibial condyles are. Some examples are shown in U.S. Pat. Nos. 4,085,466, 4,340,978 and 4,586,933, and United Kingdom Patent Application No. 7937163 (Publication No. 2 061 730), British Patent Specification No. 1 534 263. In all these constructions both the medial and lateral condylar bearing components are arranged as menisci which can move.
Analysis of removed total knee components (removed for any reason whatsoever, i.e. pain, loosening, breakage, wear, etc.) has shown that damage occurs to a much greater degree in the medial compartment of the tibial bearing surface than the lateral. Biomechanical publications have for some time claimed that the loading in the medial condyle is very much higher than in the lateral condyle.
Similarly, an analysis of used knee implants and biomechanical studies all shown that as rotation occurs in the tibia, the fore and aft sliding occurs to a greater degree in the lateral compartment than it does in the medial.